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Author Topic: Shadow Bug...  (Read 3342 times)

ncl32

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Shadow Bug...
« on: March 31, 2008, 05:08:45 am »

Hey guys just wanted to post a bit about a bug I found with the shadows on the three spheres i rendered. Heres what i did.

Created 3 identical spheres.

Colored them separate colors.

Rendered them with ART
 
and "spiky" shadowing appear as to trace the faces that are involved with with displaying a shadow on them? I don't know if its my compy or what. So, just giving you guys a heads up, Steve particularly.  ;)

nate
 
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flametiger74

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Re: Shadow Bug...
« Reply #1 on: March 31, 2008, 11:15:08 am »

Well just to let you know with ART anim8or always renders with shadows. It's a bug Steve is fixing.
Now those 3 spheres look like the just need to be subdivded.
If you don't know how to do that, than go to object mode.
click on the sphere you want to subdivide and go to Build>Subdivide at the bottom.
make sure the settings in the subdvide box are set  at 0.
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ncl32

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Re: Shadow Bug...
« Reply #2 on: March 31, 2008, 02:17:37 pm »

ROFL! Any way I actually did that... So Flametiger74, to answer your one question, yes I do know how to subdivide an object, check out my sig... But thanks for jumping on that fact that you did not know, stuff like that makes this forum great. And I know that ART always renders shadows. Which actually I kinda like that in Object mode honestly. Maybe a button to turn that on and off in Object mode would be nice. But what I was getting to was that the shadows on the spheres where not soft, or smooth. For instance I am including a render of a sphere using the scanline renderer. As you can see the shadow belts around the object quite nicely with no harsh random triangular artifacts in the shadow belt as you can see in my first ART render. And that my sir is what I was concerned about. lol

Oh yeah and the project was out of complete boredom at 1:30 at in the morning, and the second render included with this post is the final. I was doing so to come up with a good looking scene setup with nice lighting, and something that didnt use many lights. As for the random sphere cluster, that turned into a Chrome like material, High Gloss Car Paint Mimic, and A Simple Glass Material. Betcha can guess what I have in the works. Lets just say this. It has four wheels and is driven by an engine...lol

Any way thanks for you concern, but as the topic originally started off as, Steve is there any way of fixing this? Im about to do some more test renders to see if it occurs on any other low poly model of sorts.
Thanks.

Nate
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Steve

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Re: Shadow Bug...
« Reply #3 on: March 31, 2008, 06:51:29 pm »

This rendering artifact is caused by an inconsistency in the geometry and shading of your object.  Ray tracing is based on modeling a physical world.  The only 100% correct way to do ray tracing is to model all triangles as flat faces.  When smooth shading is used (like in Anim8or) you are essentially lying to the ray tracer.  The surface is not smoothly curved and yet you want it to appear that it is.  So ther ray tracer distorts the normal used for lighting.  This is inconsistent.

The scanline renderer is able to avoid much of this problem by moving the shadows backwards into the object.  It is not perfect and works OK as long as you can't see the back (like with reflections).  There is even a parameter that you can set to control how far to push the shadows.  That hack doesn't work so well for ray tracing.

The best way to avoid these artifacts is to use more faces on curved surfaces (by subdivision or simply setting the polygon count higher for a parameteric object like a sphere).
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CobraSpectre

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Re: Shadow Bug...
« Reply #4 on: March 31, 2008, 11:23:49 pm »

Steve, I assume you're talking about the Shadow Bias setting. How does this work and is it used for raytracing?
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ncl32

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Re: Shadow Bug...
« Reply #5 on: April 01, 2008, 01:48:46 am »

Hey thanks Steve, glad you would explain that. I realized that after tinkering around and doing a little research. Im typing all this all on my psp.nothings better than having the Anim8or website in the palm of my hand. Yet again, thank u Steve.
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Steve

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Re: Shadow Bug...
« Reply #6 on: April 01, 2008, 06:05:10 am »

The Shadow Bias setting is mpt currently used by the Art ray tracer.  The concept doesn't extend well to ray tracing since movig the shadow backwards only looks OK from the front.  It could appear very much worse from the point of view of a reflection.  I use other techniques to try and avoid the problem here (but I suspect that they are the cause of the shadow problems shown in other posts.)
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